Field of the Invention
Embodiments of the present invention relate generally to a method for correcting drift of a charged particle beam and a charged particle beam writing apparatus, and more specifically, relate to, for example, a method for correcting position drift of an electron beam in a writing apparatus that writes a predetermined pattern on a target object with electron beams.
Description of Related Art
The lithography technique that advances miniaturization of semiconductor devices is extremely important as a unique process whereby patterns are formed in semiconductor manufacturing. In recent years, with high integration of LSI, the line width (critical dimension) required for semiconductor device circuits is decreasing year by year. For forming a desired circuit pattern on such semiconductor devices, a master or “original” pattern (also called a mask or a reticle) of high accuracy is needed. Thus, the electron beam (EB) writing technique, which intrinsically has excellent resolution, is used for producing such a high-precision master pattern.
FIG. 11 is a conceptual diagram explaining operations of a variable-shaped electron beam writing or “drawing” apparatus. The variable-shaped electron beam (EB) writing apparatus operates as described below. A first aperture plate 410 has a quadrangular aperture 411 for shaping an electron beam 330. A second aperture plate 420 has a variable shape aperture 421 for shaping the electron beam 330 having passed through the aperture 411 of the first aperture plate 410 into a desired quadrangular shape. The electron beam 330 emitted from a charged particle source 430 and having passed through the aperture 411 is deflected by a deflector to pass through a part of the variable shape aperture 421 of the second aperture plate 420, and thereby to irradiate a target object or “sample” placed on a stage which continuously moves in one predetermined direction (e.g., the x direction) during writing. In other words, a quadrangular shape that can pass through both the aperture 411 of the first aperture plate 410 and the variable shape aperture 421 of the second aperture plate 420 is used for pattern writing in a writing region of the target object 340 on the stage continuously moving in the x direction. This method of forming a given shape by letting beams pass through both the aperture 411 of the first aperture plate 410 and the variable shape aperture 421 of the second aperture plate 420 is referred to as a variable shaped beam (VSB) system.
When writing is started, for example, a reflected electron is generated by irradiation of electron beams onto a target object. The generated reflected electron collides with the optical system of a writing apparatus, a sensor, etc., and is charged up to generate a new electric field. Then, the trajectory of the electron beam deflected toward the target object is changed by the generated new electric field. Therefore, at the time of writing, change of the trajectory of the electron beam, namely beam position drift, occurs due to the factor described above as an example. Since beam position drift is not constant, it is difficult to correct drift by prediction without measuring. Therefore, conventionally, the amount of beam position drift is measured and corrected at intervals of a certain period of time (refer to, e.g., Japanese Patent Application Laid-open No. 2011-066054).
For measuring the amount of beam position drift, conventionally, a positional deviation amount at the center of the deflection region of the deflector which deflects the beam is measured. However, there is a problem in that, in association with recent miniaturization of patterns, even if drift correction is performed based on the measured result by the conventional method, correction residue remains. Therefore, it is difficult to perform highly accurate writing. Hence, with recent miniaturization and higher integration of patterns, there is necessity of further reducing the amount of positional deviation due to beam position drift. However, conventionally, an effective method has not been established.